Engagement probe and apparatuses configured to engage a conductive pad

ABSTRACT

A method of engaging electrically conductive test pads on a semiconductor substrate having integrated circuitry for operability testing thereof includes: a) providing an engagement probe having an outer surface comprising a grouping of a plurality of electrically conductive projecting apexes positioned in proximity to one another to engage a single test pad on a semiconductor substrate; b) engaging the grouping of apexes with the single test pad on the semiconductor substrate; and c) sending an electric signal between the grouping of apexes and test pad to evaluate operability of integrated circuitry on the semiconductor substrate. Constructions and methods are disclosed for forming testing apparatus comprising an engagement probe having an outer surface comprising a grouping of a plurality of electrically conductive projecting apexes positioned in proximity to one another to engage a single test pad on a semiconductor substrate.

RELATED PATENT DATA

This patent resulted from a continuation application of priorapplication Ser. No. 08/962,229, filed on Oct. 31, 1997, now U.S. Pat.No. 6,124,721, entitled “Method of Testing The Operability of IntegratedCircuitry Of A Substrate by Engaging Electrically Conductive Test PadsOn The Substrate”; which was a continuation application of U.S.application Ser. No. 08/621,157, filed on Mar. 21, 1996, now abandoned,entitled “Method of Testing The Operability of Integrated Circuitry Of ASubstrate by Engaging Electrically Conductive Test Pads On TheSubstrate”; which was a continuation application of U.S. applicationSer. No. 08/206,747, filed on Mar. 4, 1994, entitled “Method andApparatus For Testing Semiconductor Circuitry For Operability” now U.S.Pat. No. 5,523,697; which was a divisional application of U.S.application Ser. No. 08/116,394, filed Sep. 3, 1993, entitled “A TestingApparatus For Engaging Electrically Conductive Test Pads On aSemiconductor Substrate Having Integrated Circuitry For OperabilityTesting Thereof”, now U.S. Pat. No. 5,326,428; by the following namedinventors: Warren M. Farnworth; Malcom Grief; and Gurtej S. Sandhu; thedisclosures of which are all incorporated herein by reference.

TECHNICAL FIELD

This invention relates to methods for testing semiconductor circuitryfor operability, and to constructions and methods of forming testingapparatus for operability testing of semiconductor circuitry.

BACKGROUND OF THE INVENTION

This invention grew out of the needs and problems associated withmulti-chip modules, although the invention will be applicable in othertechnologies associated with circuit testing and testing apparatusconstruction. Considerable advancement has occurred in the last fiftyyears in electronic development and packaging. Integrated circuitdensity has and continues to increase at a significant rate. However bythe 1980's, the increase in density in integrated circuitry was notbeing matched with a corresponding increase in density of theinterconnecting circuitry external of circuitry formed within a chip.Many new packaging technologies have emerged, including that of“multichip module” technology.

In many cases, multichip modules can be fabricated faster and morecheaply than by designing new substrate integrated circuitry. Multichipmodule technology is advantageous because of the density increase. Withincreased density comes equivalent improvements in signal propagationspeed and overall device weight unmatched by other means. Currentmultichip module construction typically consists of a printed circuitboard substrate to which a series of integrated circuit components aredirectly adhered.

Many semiconductor chip fabrication methods package individual dies in aprotecting, encapsulating material. Electrical connections are made bywire bond or tape to external pin leads adapted for plugging intosockets on a circuit board. However, with multichip moduleconstructions, non-encapsulated chips or dies are secured to asubstrate, typically using adhesive, and have outwardly exposed bondingpads. Wire or other bonding is then made between the bonding pads on theunpackaged chips and electrical leads on the substrate.

Much of the integrity/reliability testing of multichip module dies isnot conducted until the chip is substantially complete in itsconstruction. Considerable reliability testing must be conducted priorto shipment. In one aspect, existing technology provides temporary wirebonds to the wire pads on the die for performing the various requiredtests. However, this is a low-volume operation and further requires thetest bond wire to ultimately be removed. This can lead to irreparabledamage, thus effectively destroying the chip.

Another prior art test technique uses a series of pointed probes whichare aligned to physically engage the various bonding pads on a chip. Oneprobe is provided for engaging each bonding pad for providing a desiredelectrical connection. One drawback with such testing is that the pinsundesirably on occasion penetrate completely through the bonding pads,or scratch the bonding pads possibly leading to chip ruin.

It would be desirable to overcome these and other drawbacks associatedwith testing semiconductor circuitry for operability.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic representation of a fragment of a substrateprocessed in accordance with the invention.

FIG. 2 is a view of the FIG. 1 substrate fragment at a processing stepsubsequent to that shown by FIG. 1.

FIG. 3 is a perspective view of the FIG. 2 substrate fragment.

FIG. 4 is a view of the FIG. 1 substrate fragment at a processing stepsubsequent to that shown by FIG. 2.

FIG. 5 is a view of the FIG. 1 substrate fragment at a processing stepsubsequent to that shown by FIG. 4.

FIG. 6 is a perspective view of the FIG. 5 substrate fragment.

FIG. 7 is a view of the FIG. 1 substrate fragment at a processing stepsubsequent to that shown by FIG. 5.

FIG. 8 is a view of the FIG. 1 substrate fragment at a processing stepsubsequent to that shown by FIG. 7.

FIG. 9 is a perspective view of a substrate fragment processed inaccordance with the invention.

FIG. 10 is a view of a substrate fragment processed in accordance withthe invention.

FIG. 11 is a view of the FIG. 10 substrate fragment at a processing stepsubsequent to that shown by FIG. 10.

FIG. 12 is a view of the FIG. 10 substrate fragment at a processing stepsubsequent to that shown by FIG. 11.

FIG. 13 is a view of the FIG. 10 substrate fragment at a processing stepsubsequent to that shown by FIG. 12.

FIG. 14 is a view of the FIG. 13 substrate in a testing method inaccordance with the invention.

FIG. 15 is a view of a substrate fragment processed in accordance withthe invention.

FIG. 16 is a view of the FIG. 15 substrate fragment at a processing stepsubsequent to that shown by FIG. 15.

FIG. 17 is a view of the FIG. 15 substrate fragment at a processing stepsubsequent to that shown by FIG. 16.

FIG. 18 is a view of a substrate fragment processed ia accordance withthe invention.

FIG. 19 is a view of the FIG. 18 substrate fragment at a processing stepsubsequent to that shown by FIG. 18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

In accordance with one aspect of the invention, a method of engagingelectrically conductive test pads on a semiconductor substrate havingintegrated circuitry for operability testing thereof comprises thefollowing sequential steps:

providing an engagement probe having an outer surface comprising agrouping of a plurality of electrically conductive projecting apexespositioned in proximity to one another to engage a single test pad on asemiconductor substrate;

engaging the grouping of apexes with the single test pad on thesemiconductor substrate; and

sending an electric signal between the grouping of apexes and test padto evaluate operability of integrated circuitry on the semiconductorsubstrate.

In accordance with another aspect of the invention, a method of forminga testing apparatus for engaging electrically conductive test pads on asemiconductor substrate having integrated circuitry for operabilitytesting thereof, comprises the following steps:

providing a locally substantially planar outer surface of a firstmaterial on a semiconductor substrate;

providing a layer of second material atop the substantially planar outersurface of first material, the second material being capable ofsubstantially masking the underlying first material;

patterning and etching the layer of second material to selectivelyoutwardly expose the first material and define a grouping of discretefirst material masking blocks, the discrete first material maskingblocks of the grouping having respective centers, the respective centersof the grouping being positioned in sufficient proximity to one anothersuch that the centers of the grouping fall within confines of a givensingle test pad which the apparatus is adapted to electrically engage;

forming projecting apexes beneath the masking blocks at the maskingblock centers, the projecting apexes forming a group falling within theconfines of the given single test pad of which the apparatus is adaptedto electrically engage;

removing the discrete first material masking blocks from the substrateafter the exposing step; and

rendering the projecting apexes electrically conductive.

In accordance with yet another aspect of the invention, a testingapparatus for engaging electrically conductive test pads on asemiconductor substrate having integrated circuitry for operabilitytesting thereof comprises:

a test substrate; and

an engagement probe projecting from the test substrate to engage asingle test pad on a semiconductor substrate having integrated circuitryformed in the semiconductor substrate, the engagement probe having anouter surface comprising a grouping of a plurality of electricallyconductive projecting apexes positioned in sufficient proximity to oneanother to collectively engage the single test pad.

The discussion proceeds initially with description of methods forforming testing apparatus in accordance with the invention, and totesting apparatus construction. FIG. 1 illustrates a semiconductorsubstrate fragment 10 comprised of a bulk substrate 12, preferablyconstituting monocrystalline silicon. Substrate 12 includes a locally.substantially planar outer surface 14 comprised of a first material. Ina preferred and the described embodiment, the first material constitutesthe material of bulk substrate 12, and is accordingly silicon. A layer16 of second material is provided atop the planar outer surface 14 ofthe first material. The composition of the second material is selectedto be capable of substantially masking the underlying first materialfrom oxidation when the semiconductor substrate is exposed to oxidizingconditions. Where the underlying first material comprises silicon, anexample and preferred second material is Si₃N₄. A typical thickness forlayer 16 would be from about 500 Angstroms to about 3000 Angstroms, withabout 1600 Angstroms being preferred.

Referring to FIGS. 2 and 3, second material layer 16 is patterned andetched to selectively outwardly expose the first material and define agrouping of discrete first material masking blocks 18, 20, 24 and 26.For purposes of the continuing discussion, the discrete first materialmasking blocks of the grouping have respective centers. The lead linesin FIG. 2 depicting each of blocks 18, 20, 22 and 24 point directly tothe lateral centers of the respective blocks. The respective centers ofthe grouping are positioned in sufficient proximity to one another suchthat the centers of the grouping will fall within the confines of agiven single test pad of which the apparatus is ultimately adapted toelectrically engage for test. Such will become more apparent from thecontinuing discussion.

As evidenced from FIG. 3, masking blocks 18, 20, 24 and 26 are patternedin the form of lines or runners integrally joined with other maskingblocks/lines 28, 30, 32 and 34. The blocks/lines interconnect as shownto form first and second polygons 36, 38, with polygon 38 being receivedentirely within polygon 36. Polygons 36 and 38 constitute a grouping 41masking blocks the confines of which fall Is within the area of a givensingle test pad of which the apparatus is ultimately adapted toelectrically engage for test.

Referring to FIG. 4, semiconductor substrate 10 is exposed to oxidizingconditions effective to oxidize the exposed outer surfaces of firstmaterial. Such oxidizes a sufficient quantity of first material in asomewhat isotropic manner to form projecting apexes 40, 42, 44 and 46forming a group 43 which, as a result of the patterning of the preferrednitride layer 16, fall within the confines of the given single test padof which the apparatus is adapted to electrically engage. Such producesthe illustrated oxidized layer 48. Example oxidizing conditions toproduce such effect would be a wet oxidation, whereby oxygen is bubbledthrough H₂O while the substrate is exposed to 950° C.

Referring to FIG. 5, the oxidized first material 48 is stripped from thesubstrate. Example conditions for conducting such stripping wouldinclude a hot H₃PO₄ wet etch. Thereafter, the discrete first materialmasking blocks 18, 20, 24, 26, 28, 30, 32 and 34 are removed from thesubstrate. An example condition for such stripping in a manner which isselective to the underlying silicon apexes include a room temperature HFwet etch. Thus referring to FIG. 6, the steps of patterning and etching,exposing, and stripping form projecting apexes beneath the maskingblocks at the masking block centers, such projecting apexes beingnumbered 40, 42, 44, 46, 48, 50, 52 and 54, which are in the form ofmultiple knife-edge lines. The knife-edge lines interconnect to form theillustrated polygons 36 and 38. The apexes and correspondinglyknife-edged or pyramid formed polygons are sized and positioned insufficient proximity to fall within the confines of a single test pad ofwhich the apparatus is adapted to engage, as will be more apparent fromthe continuing discussion.

Other ways could be utilized to form projecting apexes beneath themasking blocks at the masking block centers. As but one example, a wetor dry isotropic etch in place of the step depicted by FIG. 4 could beutilized. Such etching provides the effect of undercutting more materialfrom directly beneath the masking blocks to create apexes, as such areasor regions have greater time exposure to etching.

Referring again to FIG. 5, the oxidation step produces the illustratedapexes which project from a common plane 56. For purposes of thecontinuing discussion, the apexes can be considered as having respectivetips 58 and bases 60, with bases 60 being coincident with common plane56. For clarity, tip and base pairs are numbered only with reference toapexes 40 and 42. Bases 60 of adjacent projecting apexes are spaced fromone another a distance sufficient to define a penetration stop plane 62therebetween. Example spacings between apexes would be 1 micron, whilean example length of an individual stop plane would be from 3 to 10microns. The function of penetration stop plane 62 will be apparent fromthe continuing discussion. A tip 58 and base 60 are provided at aprojecting distance apart which is preferably designed to be aboutone-half the thickness of the test pad which the given apparatus isadapted to engage.

Multiple oxidizing and stripping steps might be conducted to furthersharpen and shrink the illustrated projecting apexes. For example andagain with reference to FIG. 4, the illustrated construction in suchmultiple steps would have layer 48 stripped leaving the illustratedmasking blocks in place over the apexes. Then, the substrate would besubjected to another oxidation step which would further oxidizesubstrate first material 12, both downwardly and somewhat laterally inthe direction of the apexes, thus likely further sharpening the apexes.Then, the subsequently oxidized layer would be stripped from thesubstrate, thus resulting in deeper, sharper projections relative from aprojecting plane. Referring to FIG. 7, apex group 43 is covered anitride masking layer 64 and photopatterned. Referring to FIG. 8,silicon substrate 12 is then etched into around the masked projectingapexes to form a projection 64 outwardly of which grouping 43 of theprojecting apexes project. The masking material is then stripped.

More typically, multiple groups of projecting apexes and projectionswould be provided, with each being adapted to engage a given test pad ona particular chip. Further tiering for producing electricallycontact-engaging probes might also be conducted. FIG. 9 illustrates sucha construction having apex groups 43 a and 43 b formed atop respectprojection 64 a and 64 b. A typical projecting distance from base 60 totip 58 would be 0.5 microns, with a projection 64 being 100 microns deepand 50 microns wide. Projections 64 a and 64 b in turn have been formedatop elongated projections 66 a and 66 b, respectively. Such provideseffective projecting platforms for engaging test pads as will beapparent from the continuing discussion.

Next, the group of projecting apexes is rendered electricallyconductive, and connected with appropriate circuitry for providing atesting function. The discussion proceeds with reference to FIGS. 10-13for a first example method for doing so. Referring first to FIG. 10, asubstrate includes a pair of projections 64 c and 64 d having respectiveoutwardly projecting apex groups 43 c and 43 d. A layer of photoresistis deposited atop the substrate and patterned to provide photoresistblocks 68 as shown. Photoresist applies atop a substrate as a liquid,thus filling valleys in a substrate initially and not coating outermostprojections. Thus, the providing of photoresist to form blocks 68 isconducted to outwardly exposed projecting apex groups 43 c and 43 d, aswell as selected area 70 adjacent thereto. Photoresist blocks 68 coversselected remaining portions of the underlying substrate.

Referring to FIG. 11, electric current is applied to substrate 12 to beeffective to electroplate a layer of metal 72 onto outwardly exposedprojecting apex groupings 43 c and 43 d and adjacent area 70. An examplematerial for layer 72 would be electroplated Ni, Al, Cu, etc. An examplevoltage and current where substrate 12 comprises silicon would be 100Vand 1 milliamp, respectively. Under such conditions, photoresistfunctions as an effective insulator such that metal deposition onlyoccurs on the electrically active surfaces in accordance withelectroplating techniques. Photoresist is then stripped from thesubstrate, leaving the FIG. 11 illustrated construction shown, which mayalso include a desired conductive runner 74 formed atop bulk substrate12 between projections 64 c and 64 d.

The preferred material for metal layer 72 is platinum, due to itsexcellent oxidation resistance. Unfortunately, it is difficult todirectly bond the typical copper or gold bonding wires to platinum.Accordingly, preferably an intervening aluminum bonding site isprovided. Referring to FIG. 12, an aluminum or aluminum alloy layer 76is blanket deposited atop the substrate. A layer of photoresist isdeposited and patterned to provide photoresist masking blocks 78. Thesubstrate would then be subjected to an etch of the aluminum material ina manner which was selective to the underlying platinum. Example etchingconditions would include a hot H ₃PO₄ wet etch. Such leaves resultingelevated bonding blocks 80 of aluminum atop which a bonding wire 82 isconventionally bonded, as shown in FIG. 13.

The description proceeds with reference to FIG. 14 for utilizing such anapparatus for conducting electrical tests of a chip. FIG. 14 illustratesthe testing apparatus of FIG. 13 engaging a chip 85 which is beingtested. Chip 85 comprises a substrate portion 86 and outwardly exposedbonding pads 88. Protecting or encapsulating material 90 is providedsuch that substrate 86 and circuitry associated therewith is protected,with only bonding pads 88 being outwardly exposed. Bonding pads 88 havesome thickness “A”.

Substrate 12 comprises a test substrate having engagement probes 64 cand 64 d projecting therefrom. Such include respective electricallyconductive apexes groups 43 c and 43 d positioned in respectiveproximity to fall within the confines of and engage a single test pad 88on chip 85. Such apexes are engaged with the respective test pads, asshown.

The illustrated projecting apexes actually project in to half-way intothe thickness of the bonding pads, a distance of approximately on-half“A”. The penetration stop surface 62 described with reference to FIG. 5provides a stopping point for preventing the projecting points fromextending further into bonding pads 88 than would be desired. Inconnecting the testing apparatus to chip 85, pressure would be monitoredduring engagement of the projecting tips relative to the pads 88. Atsome point during the projection, the force or back pressure against thetesting apparatus would geometrically increase as the penetration stopplane reaches the outer surface of the bonding pads 88, indicating thatfull penetration had occurred. At this point, the testing substrate andchip 85 would be effectively electrically engaged. An electric signalwould be sent between the respective grouping of apexes and respectivetest pads in conventional testing methods to evaluate operability ofintegrated circuitry formed within the semiconductor substrate 85.

Reference is made to FIGS. 15-17 for a description of an alternatemethod of rendering projecting apexes electrically conductive.

Starting with FIG. 15, such are sectional views taken laterally throughprojection 64 a of FIG. 9. Referring to FIG. 16, an electricallyconductive nucleation layer 90 is blanket deposited atop the apexes andsubstrate. An example material would be elemental nickel deposited bysputter techniques. Photoresist is then applied and patterned as shownto produce photoresist blocks 92. Thus, the nucleation layer coatedprojecting apexes and selected area adjacent thereto is outwardlyexposed, while selected remaining nucleation layer coated portions ofthe substrate are coated by resist blocks 92. At this point, a currentis applied to nucleation layer 90 effective to electrodeposit a layer94, such as electroless deposited copper, to a thickness of 1 micron.Resist blocks 92 effectively insulate underlying nucleation layer 90from depositing copper atop the resist. An example voltage and currentwould be 5 V and 1 milliamp, respectively.

Referring to FIG. 17, the resist is then stripped from the substrate. Adry plasma etch is then conducted which selectively removes the exposednickel nucleation layer 90 relative to copper layer 94, such that onlycopper over the illustrated nickel remains. Then if desired and asshown, current is applied to the nucleation layer and copper material ina manner and under conditions which electroless deposits a 2000 Angstromthick layer 96 of, for example, platinum, palladium or iridium. Wirebonding could then be conducted apart from apexes 43 a utilizing anintervening block of aluminum.

Such technique is preferable to the previously described electrolessdeposition method in that lower voltage and current can be utilized inthe electroless deposition method where a highly conductive nucleationlayer is provided atop the substrate.

Another alternate and preferred technique for forming and rendering theprojecting apexes conductive is shown with reference to FIGS. 18 and 19.Such is an alternate construction corresponding to that constructionshown by FIG. 10. FIG. 18 is the same as FIG. 10, but for the additionof, a) an insulating layer 71, preferably SiO₂; and b) a metalnucleation layer 73, prior to the providing and patterning to producephotoresist blocks 68. Such a process is preferable to that shown byFIG. 10 to provide separation of the typical monocrystalline siliconsubstrate 12 from direct contact with metal. FIG. 19 illustrates thesubsequent preferred electroless deposition of a metal layer 72 usingsubstrate nucleation layer 73 as a voltage source. With respect to theembodiment shown by FIGS. 15-17, such also would preferably be providedwith an insulating layer prior to deposition of the nucleation layer. Analternate and preferred material for layer 73 would be aluminum metal,with the subsequently electroless layer being comprised essentially ofplatinum. Platinum could then be used as a masking layer to etch exposedaluminum after photoresist strip. An example etch chemistry for suchetch would include a wet H₃PO₄ dip.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. An apparatus configured to engage a conductivepad of an electrical component, the apparatus comprising: a substrate;and an engagement probe comprising a semiconductor material andconfigured to project from the substrate, the engagement probe having anouter surface comprising a plurality of apexes having an outerconductive layer configured to engage the conductive pad.
 2. Theapparatus of claim 1 wherein the apexes are provided at a commonelectrical potential.
 3. The apparatus of claim 1 wherein the engagementprobe includes at least one of the apexes in the shape of a knife-edgeline.
 4. The apparatus of claim 1 wherein the engagement probe is formedon a projection from the substrate.
 5. The apparatus of claim 1 whereinat least one of the apexes has a selected projecting distance, theprojecting distance being about one-half the thickness of the conductivepad which the apparatus is adapted to engage.
 6. The apparatus of claim1 wherein at least one of the apexes projects from a penetration stopplane.
 7. The apparatus of claim 1 wherein at least one of the apexes issubstantially electrically insulated from the substrate.
 8. An apparatusconfigured to engage a conductive pad of an electrical component, theapparatus comprising: a substrate; and an engagement probe comprising asemiconductor material and configured to project from the substrate, theengagement probe having an outer surface comprising a plurality ofelectrically conductive projecting apexes provided at a commonelectrical potential and configured to extend elevationally above anuppermost surface of the substrate and to engage the conductive pad. 9.The apparatus of claim 8 wherein the engagement probe includes theapexes in the shape of knife-edge lines.
 10. The apparatus of claim 8wherein the engagement probe is formed on a projection from thesubstrate.
 11. The apparatus of claim 8 wherein the apex has a selectedprojecting distance, the projecting distance being about one-half thethickness of the conductive pad which the apparatus is adapted toengage.
 12. The apparatus of claim 8 wherein the apexes project from apenetration stop plane.
 13. The apparatus of claim 8 wherein theengagement probe comprises a conductive layer provided over the apexes.14. The apparatus of claim 8 wherein the apexes are substantiallyelectrically insulated from the substrate.
 15. An apparatus configuredto engage a conductive pad of an electrical component containingintegrated circuitry coupled with the conductive pad, the apparatuscomprising: a substrate; and an engagement probe fabricated from asemiconductor material and configured to project from the substrate, theengagement probe having an outer surface comprising an electricallyconductive projecting apex configured to engage the conductive pad andto at least one of apply and receive electrical signals through theconductive pad with respect to the integrated circuitry; wherein theouter surface includes a plurality of apexes in the shape of knife-edgelines, the knife-edge lines being positioned to form at least one fullyenclosed polygon.
 16. The apparatus of claim 15 wherein the knife-edgelines are positioned to form at least two polygons one of which isreceived entirely within the other.